Light

Question 1

Normal

Answer 1

A line drawn at 90° (perpendicular) to the surface at the point of incidence (where the ray hits the mirror)

Question 2

Angle of incidence (i)

Answer 2

The angle between the incident ray and the normal

Question 3

Angle of reflection (r)

Answer 3

The angle between the reflected ray and the normal

Question 4

characteristics of an image formed in a vertical plane mirror (compared to the object) (5)

Answer 4

• The same size as the object
• The same distance behind the mirror as the object is in front
• Laterally inverted (left and right reversed)
• Virtual (cannot be projected onto a screen)
• Upright

Question 5

Law of reflection

Answer 5

Angle of incidence = Angle of reflection
i = r
(Remember both are measured from the normal not the surface)

Question 6

Why are images fromed in a plane mirror considered virtual?

Answer 6

It’s virtual because the reflected rays appear to come from behind the mirror but do not actually meet there. The image cannot be projected onto a screen

Question 7

How do you use diagrams, measurements, and calculations for reflection in plane mirrors?

Answer 7

• draw the mirror as a straight line with diagonal lines coming off the top
• draw the incident ray and the reflected ray
• use a protractor to measure angles from the normal
• make sure that ∠i = ∠r
• use a ruler
• extend reflected rays backward with dashed lines to locate the virtual image

Question 8

Refraction

Answer 8

The change in direction of a light ray passing from one medium to another

Question 9

Refractive index (n)

Answer 9

The ratio of the speeds in two different wave regions

Question 10

n equation

Answer 10

n = sin i/ sin r

Question 11

Total internal reflection

Answer 11

• total internal reflection (TIR) occurs when a ray of light travels from a more dense medium to a less dense medium - glass to air
• the angle of incidence is greater than the critical angle
• no refraction occurs — the light is completely reflected inside the more dense medium

Question 12

Real images (4)

Answer 12

• image is formed when rays of light meet at a point after reflection/refraction
• it is formed on the different side as that of the object
• inverted
• can be projected/obtained on a screen

Question 13

Virtual images (4)

Answer 13

• the image is formed when rays of light appear to meet (when diverging rays are extended) at a point
• it’s formed on the same side as the object
• upright
• cannot be obtained/projected on a screen

Question 14

Local mean time

Answer 14

less dense —> more dense —> towards normal

Question 15

Describe the passage of light through a transparent material (limited to the boundaries between two media only)

Answer 15

• light changes speed at the boundary between the 2 media, causing refraction
• from air to glass (less dense → more dense):
  → light slows down and bends towards the normal
• from glass to air (more dense → less dense):
  → light speeds up and bends away from the normal

Question 16

How to draw total internal reflection on a ray diagram

Answer 16

• draw the shape of the more dense medium - this is the boundary between the 2 media
• draw the normal line (a dashed line) - the point where the light hits the boundary
• draw the incident ray inside the glass, coming toward the boundary at a steep angle (greater than the critical angle)
• draw the reflected ray inside the glass, bouncing off the boundary at the same angle as the incident ray (angle of reflection = angle of incidence)

-do NOT draw any refracted ray going into the air, because in TIR, light does not pass through the boundary

• label the incident ray, reflected ray, normal, and the boundary

Question 17

Critical angle

Answer 17

The angle of incidence at which the angle of refraction is 90* and above which all light is totally internally reflected

Question 18

Describe total internal reflection in optical fibres

Answer 18

• total internal reflection (TIR) happens inside an optical fibre because light travels through the core (more dense material) and hits the boundary with the cladding (less dense material) at an angle greater than the critical angle
• this causes light to be completely reflected inside the fibre without escaping

Question 19

state some common applications of optical fibres

Answer 19

• telecommunications - transmitting telephone and internet signals
• medicine - in endoscopes to see inside the body

-lighting and sensors - for decorations and detecting changes in conditions

Question 20

Describe the action of a thin converging lens on a parallel beam of light.

Answer 20

• A thin converging lens refracts parallel rays of light so that they converge at a point called the principal focus (focal point)
• Rays from a distant object can be assumed to be parallel

Question 21

Principal axis

Answer 21

A straight line passing through the center of the lens and perpendicular to it

Question 22

Principal focus (focal point)

Answer 22

The point where parallel rays of light meet after passing through the lens

Question 23

Focal length

Answer 23

The distance from the center of the lens to the principal focus

Question 24

Draw and use ray diagrams for the formation of an image by a thin converging lens (real images only)

Answer 24

• Draw the principal axis, lens, and principal focus points
• Draw rays from the top of the object:
• Parallel ray refracted through the principal focus (and then down through F on the other side of the lens)
• Ray through the center of the lens goes straight
• The rays meet ( pass through the parallel refracted ray) on the other side of the lens to form a real image

Question 25

Describe the characteristics of an image using the terms enlarged / same size / diminished and upright / inverted

Answer 25

- Enlarged: Image is bigger than the object. - Same size: Image is the same size as the object. - Diminished: Image is smaller than the object. - Upright: Image has the same orientation as the object. - Inverted: Image is upside down compared to the object.

Question 26

Draw and use ray diagrams for the formation of a virtual image by a thin converging lens

Answer 26

- When the object is between the lens and the principal focus, rays appear to diverge after the lens - Extend the rays backward to meet on the same side as the object to form a virtual image - The virtual image is upright and enlarged

Question 27

Describe the characteristics of an image using the terms real and virtual

Answer 27

- real image: formed where rays actually meet, can be projected on a screen, usually inverted - virtual image: formed where rays only appear to meet, cannot be projected, usually upright

Question 28

Describe the use of a single lens as a magnifying glass

Answer 28

A magnifying glass is a thin converging lens used to produce a virtual, enlarged, and upright image of an object placed closer than the focal length to the lens. This makes small objects appear bigger for detailed viewing.

Question 29

seven colours of the visible spectrum in order of frequency and in order of wavelength

Answer 29

Order of increasing frequency: Red → Orange → Yellow → Green → Blue → Indigo → Violet Order of decreasing wavelength: Red → Orange → Yellow → Green → Blue → Indigo → Violet

Question 30

Describe the dispersion of light as illustrated by the refraction of white light by a glass prism

Answer 30

When white light passes through a glass prism, it bends (refracts) because light changes speed in the glass. Different colours in white light bend by different amounts because each colour has a different wavelength. This separates white light into its colours, spreading them out as a spectrum — this process is called dispersion